In a U.S. Pat. No. 3,422,515, a method for making porous anodes by freezing wet powder and sintering is described. The result of this process is anodes in the presintered condition without risers. The risers are attached to presintered anodes by welding. Following the welding, the anodes are given a final sintering treatment in vacuum or inert gas atmosphere. After sintering, anodes may be attached to processing bars or stringers by welding.
Even though this process is being used successfully, numerous operations are required to fabricate anodes on stringers from tantalum powder and wire. Besides the casting of anodes from wet tantalum powder slurry in rubber molds and freezing, several steps are required to obtain presintered anodes, attach risers, resinter the anodes with risers, and finally weld the anodes with risers to stringers.
For several reasons it would be most desirable to produce anodes on stringers without the need of two sintering steps and the welding operation. Firstly, handling may introduce mechanical damage and/or contamination in sintered anodes and should be avoided. Best results are obtained if sintered anodes are kept separated from each other and are not allowed to touch any processing fixtures, equipment, or other solid structures that may result in mechanical abrasion or other damage.
Secondly, a welding operation requires a high degree of accuracy in positioning the leads on the anode. Elaborate mechanization is needed for efficient parts handling at this stage.
Thirdly, during final sintering anodes are stacked in crucibles and some degree of sintering between anodes is unavoidable. The resulting inter-anode bonds have to be broken by force which is thought to be harmful to consistent electrical characteristics of finished capacitor devices.
It is an object of the present invention to reduce the number of steps required for the production of capacitor anodes.
It is another object of the present invention to provide an easier method of attaching risers to anodes for capacitors.
It is another object of the invention to reduce the number of sintering steps.
It is another object of the present invention to avoid contact of the anodes with each other and with processing fixtures.